The invention is related generally to web-processing apparatus and, more particularly, to apparatus for processing a coated web and air-turn apparatus used to support the web during processing.
In many manufacturing or processing operations material, in the form of a material web, is coated or treated with various inks, resins and other substances in order to impart desired properties to the material. Web materials processed in this manner include, for example, glass fiber, paper, film and metals. The coating process typically involves unwinding the material from a supply roll, applying the coating, drying the coated web and re-winding the coated web onto a take-up roll or otherwise processing the coated web. The coating is typically a liquid and is applied to one or both sides of the web or by impregnating the web by, for example, immersing the web in a bath or spraying the coating on the web.
An important limitation with respect to the amount of web material that can be processed during a given unit time is the rate at which the web material can be dried following coating. It is important to dry the web rapidly because wet coating can be damaged or removed by contact with rollers and other coating apparatus components. Moreover, the web material often cannot be re-wound or processed further until the web coating has dried to a predetermined extent.
Web dryers are commonly used to process the coated web. The dryer increases the rate at which the coating is dried thereby increasing the rate at which the web can be processed. Typically, the web dryer is positioned along the path of the moving web downstream of the coating apparatus and may include air jets or heat sources to dry the web coating. In coating operations known as xe2x80x9cpre-pregxe2x80x9d coating operations, the web is moved through the dryer following coating at rates ranging from about 40-80 feet/minute to as high as 100 feet/minute. In other coating and processing operations the web speed may be much greater. The path of the web through the dryer can be as long as required to adequately dry the coating.
While web dryers are highly effective at increasing the rate at which the coating dries, they are not without certain disadvantages. One potential disadvantage is that dryers have a large footprint and occupy a significant amount of floor space at the operator""s facility. One solution to this dryer-size-related problem is to provide plural parallel drying sections (rather than a single linear dryer section) and direction-changing apparatus to direct the web through the parallel dryer sections. Such an arrangement can reduce the amount of space required for the dryer.
In vertical dryers, cylindrically shaped, chilled rollers are used to change the direction of web movement. Chill rollers are well known and are commercially available, for example, from the F.R. Gross Company of Stow, Ohio. After initial drying in a first vertically-oriented drying section the web is then directed over, for example, paired chill rollers, through a 180xc2x0 direction change, and through a second vertically-oriented drying section to complete the drying process. In such an operation, the web comes into direct physical contact with the chill rollers as the direction of web movement changes.
However, the use of such direction-changing chill rollers may be less than satisfactory in certain coating operations, particularly where the web is impregnated with coating material or where it is desired to apply coating to the web side facing the roller. Any such contact should be avoided because such contact can potentially damage any not-yet-dried coating material on the web. For example, the coating could, in certain circumstances, become adhered to the roller or the coating could be scraped away from the web by contact with the roller surface. Cooling of the chill roller minimizes potential adherence of coating to the roller. However, this is not a complete solution because any contact between the roller and coating creates the possibility that the coating will attach to the roller or otherwise become damaged.
In a further effort to minimize this contact-related problem, manufacturers of dryer apparatus have been required to provide refrigeration apparatus to cool the web and the web coating before the web contacts the chill roller. The refrigeration apparatus is provided in the form of a separate cooling zone or chamber adjacent the first chill roller. Refrigeration apparatus is provided to reduce the temperature in the cooling zone thereby cooling the web and web coating. Cooling of the web in this manner has been found to reduce, but not completely eliminate, adherence of coating material to the roller. As mentioned, the cooled web may be re-heated after passing over the chill rollers in order to complete the drying process.
Use of such refrigeration or chilling apparatus includes certain potential disadvantages. One potential disadvantage is that the cooling process is energy intensive both with respect to the energy required to cool the web but also with respect to the additional energy needed to reheat the cooled web in the downstream dryer sections. Another disadvantage is that alternate heating and cooling of the web reduces the rate at which the web can be processed through the dryer thereby reducing dryer efficiency. A further potential disadvantage of the cooling process is the additional cost of the refrigeration and related equipment used to cool the web.
Yet another possible disadvantage of the cooling process stems from the increased maintenance costs required to avoid potential contamination of the web as the web passes through the cooling section or sections. Contamination of the web could potentially occur as evaporating solvents and other materials (such as dirt or airborne particulates) condense and/or collect on the cool surface areas of the dryer within the cooling section. These materials can flake off and collect on the web and web coating possibly contaminating the web. Any such contamination should be avoided.
Removal and cleaning of the potential contaminates from the cooling section is a labor-intensive project which must be performed on a frequent basis increasing the cost of the coating operation. Further increasing the cost of operation is the fact that the processing line must typically be shut down for the cleaning to take place. This results in disruption of the manufacturing process.
The foregoing problems involving potential undesired contact between a support and/or direction-changing roller and a coated web surface facing the roller are present in other types of web-processing operations. For instance, in web laminating operations it is often necessary to change the direction of web movement in order to process the web, for example by steam moisturizing of the web before passage of the web into a laminator apparatus. However, conventional chill roller apparatus have proven unsatisfactory for this purpose because it is possible to change the web direction only about 180xc2x0 without contacting the coated side of the web. As a result, less-than optimal processing line configurations have been developed simply because of the inability to change web direction without contact between the roller and the coated surface of the web.
Improved web-processing apparatus which would facilitate an improvement in the quality of products manufactured in coating operations, which would facilitate the use of more compact and efficient dryers and processing equipment used in coating operations and which would generally make processing operations more efficient would represent an important advance in the art.
It is an object of this invention to provide improved web-processing apparatus overcoming some of the problems and shortcomings of the prior art.
An important object of this invention is to provide improved web-processing apparatus which includes apparatus for changing the direction of web movement yet does not require a cooling section upstream of the web direction-changing apparatus.
It is also an object of the invention to provide improved web-processing apparatus capable of making coating operations more efficient.
A further object of the invention is to provide improved web-processing apparatus which facilitate improvement in the quality of product produced in coating operations.
Yet another object of the invention is to provide improved web-processing apparatus which reduces energy consumption.
Another object is to provide improved web-processing apparatus which facilitates an increase in the rate at which web material can be dried.
Still another object of the invention is to provide improved web-processing apparatus which facilitates processing of the web with reduced potential for possible web contamination.
Yet another object of this invention is to provide improved web-processing apparatus which permits a change in the direction of web movement yet minimizes actual contact between the web and the processing apparatus.
An object of this invention is to provide improved web-processing apparatus capable of processing webs of different widths.
A further object of the invention to provide improved web-processing apparatus with an efficient design.
One additional object of the invention is to provide improved web-processing apparatus which facilitates changes in the direction of web travel.
How these and other objects are accomplished will be apparent from the following descriptions and from the drawings.
The invention comprises web-processing apparatus for processing a coated web and air-turn apparatus used to support the web during processing. The novel air-turn apparatus facilitates construction of dryers without separate cooling apparatus adjacent the air-turn apparatus and further facilitates optimal process equipment configurations.
In one embodiment, an improved web dryer including the air-turn apparatus is provided for drying a coating-impregnated web or web having a coated side facing the air-turn apparatus. The dryer is provided with a support frame having a web inlet, a web outlet and a web path between the inlet and outlet. Dryer apparatus mounted with respect to the frame, and proximate to the web, dry the coated web moving along the web path. Cooling apparatus may optionally be mounted with respect to the frame and along the web path downstream of the dryer apparatus for cooling the coated web moving along the web path after drying and before rewinding of the web or further web processing.
One or more air-turn apparatus may be mounted along the dryer frame and along the web path for changing the direction of web movement along the web path. The improved air-turn apparatus comprises a body having an outer surface defining an arcuate web flotation zone facing a coated side of the web and a plurality of openings in the body positioned along the web flotation zone.
An air-conducting conduit is preferably positioned at least partially in the body. The conduit has an inlet for receiving pressurized air and at least one outlet in communication with the body openings thereby providing a passageway through which pressurized air may be directed out of the body to form an air cushion at the web flotation zone. An air blower in communication with the conduit inlet supplies pressurized air to the air-turn apparatus. This novel arrangement permits the coated web to be flotatingly supported by the air cushion at the web flotation zone so that the coated side of the web does not directly contact the air-turn apparatus as the web passes the air-turn apparatus. There is no need to pre-chill the web because the web does not contact the air-turn apparatus.
In one preferred embodiment, the body is cylindrically-shaped and has a body axis, first and second end walls, an arcuate outer surface and the web flotation zone is positioned across a predetermined portion of the arcuate outer surface. It is preferred that the body have an inner wall surface defining a body interior. In this preferred embodiment, the body openings are in communication with the body interior.
It is most highly preferred that the body is rotatable and synchronized to rotate with the web so as to minimize any possible frictional contact between the web and the air-turn apparatus. Accordingly, the air-turn apparatus preferably includes a first mount along the body first end wall and a second mount along the body second end wall, the mounts provided for rotatably supporting the body with respect to the frame.
The preferred first mount comprises a stationary centertube and related structure described herein. The centertube is secured with respect to the frame and supports the body for rotation along an axis coaxial with the body axis. In this embodiment the centertube also serves as the conduit for directing air into the body and body openings. The centertube includes a centertube body positioned through an opening in the first end wall and at least partially in the body interior, a centertube outer surface, a centertube inner surface defining a hollow air conduit, an air inlet in communication with the air conduit and at least one air outlet in communication with the body interior. The most highly preferred body first end wall includes a fixed inner wall portion, a rotatable outer wall portion and bearing structure therebetween permitting rotation of the outer wall and air-turn apparatus body with respect to the centertube and fixed inner wall.
The preferred second mount comprises a shaft supporting the body also along the axis coaxial with the body axis. The shaft has a first end secured with respect to the second end wall for co-rotation of the shaft with the body and a second end portion rotatably secured with respect to the frame.
To promote efficient operation of the air-turn apparatus, it is highly preferred that first and second walls are positioned in the body interior to form a plenum between the centertube and body adjacent the web flotation zone. The plenum efficiently directs pressurized air from the centertube to the web flotation zone.
It is also highly preferred that one or more movably-mounted deckles be provided in the plenum for adjusting an axial dimension of the plenum and directing pressurized air to a predetermined portion of the web flotation zone. Apparatus may be provided to move each deckle within the air-turn apparatus body. Adjustment of the plenum permits the air-turn apparatus to be used with webs of different widths.
Preferably, the air-turn apparatus is chilled to prevent any possible sticking of the web coating to the air-turn apparatus in the unintended event that the web and air-turn apparatus should come into contact. Such preferred air-turn apparatus embodiment includes a coolant-conducting conduit in the air-turn apparatus body. The conduit is in heat-transfer communication with the body outer surface and has an inlet for receiving pressurized coolant and an outlet for discharging the coolant. Preferably, the coolant-conducting conduit is positioned between the body inner and outer surfaces and the coolant inlet and outlet comprise separate passageways in the second shaft. Refrigeration apparatus is preferably in fluid communication with the conduit inlet and outlet for supplying chilled coolant to the conduit. Optionally, a low-friction coating may be affixed to the body outer surface to further minimize any adherence of the coating to the air-turn apparatus.
The dryer preferably includes drive apparatus for synchronously rotating the body with the web. The drive apparatus may include a motor, linkage apparatus connecting the motor to the body and control apparatus for controlling the motor.
The air-turn apparatus may be used in various web-processing operations including, without limitation, xe2x80x9cpre-pregxe2x80x9d coating operations and lamination operations.
It should be noted that use of the terms xe2x80x9cair-turn apparatusxe2x80x9d or xe2x80x9cairxe2x80x9d throughout the application reflects the fact that the invention will most likely utilize pressurized air for purposes of creating the xe2x80x9cair cushionxe2x80x9d used to flotatingly support the web. However, these terms are not intended to be limiting because any suitable pressurized gas may be used to support the web along the novel air-turn apparatus. Indeed, air comprises a mixture of gases such as oxygen, nitrogen and carbon dioxide.
Moreover, the dryer structure and the structure of other components described herein is intended to be illustrative and not limiting. For example, the dryer web outlet and inlet are meant only to refer to locations at which the web enters and exits the dryer. The web could enter and exit the dryer at other locations and the web path could travel both inside and outside of the dryer.